It appears the Slony xxid functions are claiming to be capable of
hashing, but cannot actually do so.

sdb=# explain select query_start, current_query from pg_locks join
pg_stat_activity on pid = procpid where granted = true and transaction
in (select transaction from pg_locks where granted = false);
ERROR:  could not find hash function for hash operator 716373

-------- Forwarded Message --------
From: Tom Lane <tgl at sss.pgh.pa.us>
To: Rod Taylor <pg at rbt.ca>
Cc: PostgreSQL Development <pgsql-hackers at postgresql.org>
Subject: Re: [HACKERS] Hashagg planning bug (8.0.1)
Date: Tue, 10 May 2005 13:17:56 -0400

Rod Taylor <pg at rbt.ca> writes:
> It's the = operator that Slony adds for xxid comparisons. I didn't even
> think of changes Slony would have made.

> ssdb=# select * from pg_operator where oid = 716373;
>  oprname | oprnamespace | oprowner | oprkind | oprcanhash | oprleft | oprright | oprresult | oprcom | oprnegate | oprlsortop | oprrsortop | oprltcmpop | oprgtcmpop |    oprcode    | oprrest |  oprjoin
> ---------+--------------+----------+---------+------------+---------+----------+-----------+--------+-----------+------------+------------+------------+------------+---------------+---------+-----------
>  =       |         2200 |      588 | b       | t          |  716353 |   716353 |        16 | 716373 |    716372 |     716371 |     716371 |     716371 |     716369 | _ssrep.xxideq | eqsel   | eqjoinsel
> (1 row)

I think you need to have a word with the Slony boys.  They shouldn't be
marking the operator oprcanhash if they aren't providing a valid hash
opclass for the datatype.  Per the manual:

: To be marked HASHES, the join operator must appear in a hash index
: operator class. This is not enforced when you create the operator, since
: of course the referencing operator class couldn't exist yet. But
: attempts to use the operator in hash joins will fail at runtime if no
: such operator class exists. The system needs the operator class to find
: the data-type-specific hash function for the operator's input data
: type. Of course, you must also supply a suitable hash function before
: you can create the operator class.

			regards, tom lane

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